Hi, I find your idea very interesting, but I'm not sure I quite understand it? You want to teach the terms -Used to and-Would

If so then I think that it's somewhat simple because there aren't too many used to and would in the lyrics. Explain to them how used to refers to what you did in the past but don't necessarily do anymore. I find your idea to use Coldplay songs as teaching material a great one! They write very good songs and when I'm a teaching I would like to use songs to teach things. Keep up the good work, good luck.